The compound designated bupropion hydrochloride is described in U.S. Pat. Nos. 3,819,706 and 3,885,046. It is marketed as an anti-depressant and an aid to smoking cessation. Bupropion is an aminoketone-derivative chemically unrelated to other currently available antidepressants (e.g., selective serotonin-reuptake inhibitors, tricyclics, tetracyclics).
While the neurochemical mechanisms of the antidepressant and smoking cessation effects are unknown, noradrenergic pathways and/or dopaminergic effects appear to be primarily involved. Bupropion does not inhibit monoamine oxidase and is a weak blocker of serotonin and norepinephrine uptake.
The drug is useful in the treatment of depressive affective disorders (e.g., major depression) at dosages of 75 to 600 mg daily. Bupropion may be preferable to other agents because of its minimal anticholinergic, cardiovascular, and antihistaminic effects or in those patients who have experienced weight gain or sexual dysfunction with another antidepressant. Bupropion, as extended-release tablets, is used in the cessation of smoking at dosages of 100-300 mg daily. Withdrawal symptoms and cigarette craving are reduced with bupropion. Other uses include patients with bipolar depression, attention-deficit hyperactivity in both adult and pediatric patients, and panic symptoms superimposed on depression.
Immediate release bupropion tablets provide more than 75% of bupropion release into the dissolution media in 45 minutes. In studies to date, the risk of seizures appears to be strongly associated, in part, with the use of instant release tablets.
Numerous techniques exist in the prior art for preparing sustained or controlled release pharmaceutical formulations. One common technique involves surrounding an osmotically active drug core with a semipermeable membrane. The drug is released from the core over time by allowing a fluid such as gastric or intestinal fluid to permeate the coating membrane and dissolve the drug so the dissolved drug can permeate through the membrane. In some cases a hydrogel is employed to push the active ingredient through the passageway of the membrane.
Another common technique for preparing controlled-release pharmaceutical formulations is to encapsulate a plurality of beads, pellets or tablets that are coated with varying levels of diffusion barriers. The barriers can be of the same or different chemical composition. Release of the pharmaceutical may occur by leaching, erosion, rupture, diffusion or similar actions depending on the nature and thickness of the coating material. These products require multi-layered coating, sometimes as much as 30 to 90 coats.
Film coating techniques are characterized by the deposition of a uniform film onto the surface of a substrate. Because of the capability of depositing a variety of coating materials onto solid cores, this process has been used to make controlled release dosage forms starting from different formulations, such as tablets, granules, pellets and capsules. Cores are usually prepared using one of the following processes: compaction, surface layering, or agglomeration.
One limitation associated with these dosage forms consists in their failure to delay drug delivery. Many of the multi-walled preparations described above do not provide prolonged delayed release of the drug prior to initiation of sustained release, which is important when biphasic release profiles are desired. Other systems are essentially “delayed” releases mechanisms. There is delay of drug release in the stomach, but once the coated drug reaches the intestines, the release of medication is rapid. There is no sustained release in the intestines.
Bupropion hydrochloride is highly soluble in water with a high permeability characterized by rapid and almost complete absorption. Peak plasma concentrations occur within 2 hours for bupropion and 3 hours for bupropion sustained-release. Its biphasic pharmacokinetics is characterized by a two-compartment model; the distributive phase has a mean half-life of 3 to 4 hours with a biphasic decline and a terminal T ½ of about 14 hours following single doses. A major drawback is extensive first-pass metabolism. It appears that only a small portion of any oral dosage reaches the systemic circulation intact. Immediate-release tablets are dosed three times a day, preferably with 6 or more hours separating the doses. For those patients requiring doses greater than 300 mg daily, each divided dose should not exceed 150 mg each. This necessitates administration of the tablets 4 times daily with at least 4 hours between successive doses. Commercially available sustained-release products are available in film-coated tablets marketed by Glaxo Wellcome under the tradenames Wellbutrin® SR and Zyban®. These are dosed twice daily. For those patients requiring above 300 mg daily, the regimen remains twice daily dosing. No currently available product provides a sustained release profile suitable for once daily dosing.
Patient compliance is especially problematic in depressed patients. There is a need for improved patient compliance. One of the means employed clinically to improve patient adherence to therapy is simplification of the dosing regimen. Thus, need exists for a once daily bupropion formulation.
Sustained release tablet forms of bupropion are described in U.S. Pat. No. 5,427,798, comprising a sustained release tablet which provides peak bupropion blood levels at approximately 2-3 hours, thereby requiring twice daily dosing. Controlled release is achieved by combining bupropion particles with microcrystalline cellulose and hydrogel-forming hydroxypropyl methylcellulose.
Another sustained release bupropion tablet or caplet formulation disclosed in U.S. Pat. No. 4,687,660, comprises a difficult manufacturing process and limited shelf life. U.S. Pat. No. 5,358,970 discloses a formulation of bupropion hydrochloride that contains an acid stabilizer.
U.S. Reissue Pat. No. 33,994 discloses a tablet formulation of a water insoluble, water-permeable film coating surrounding the drug core and a particulate, water-soluble, pore-forming material dispersed within the film coating; this osmotic gradient and channel forming system is applicable for tablet dosage forms. However, here also at least twice daily dosing is necessitated by the release profile of 25-70% of bupropion within 4 hours, and 40-90% within 6 hours. Wellbutrin® SR is a commercially available twice a day dosage form of bupropion which contains carnauba wax, cysteine hydrochloride, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polyethylene glycol and titanium dioxide.
There is no capsule form of bupropion commercially available. Capsules are advantageous in those patients who have difficulty swallowing where the contents of the capsule may be sprinkled on food.
Immediate release tablets must be stored at a temperature above 15-25° C. and protected from light and moisture. Extended-release tablets should be stored in tight, light-resistant containers at a temperature of 20-25° C.
The need exists for a delayed, sustained release pharmaceutical preparation that provides a longer delay of drug dissolution thereby allowing greater flexibility in designing sustained release profiles, provides improved plasma levels wherein the maximum plasma concentration (Cmax) can be substantially reduced without a concomitant reduction in AUC, and is simply and economically produced. Such a delayed delivery dosage form has a practical application, and it represents a valuable contribution to the medical arts. The present invention provides such a composition, and offers an efficient and cost effective method of preparation.
Accordingly, it is an object of this invention to provide a sustained release formulation of bupropion suitable for once daily administration.
Another object of the present invention is to provide a capsule dosage form comprising means for delaying delivery of the drug in gastric fluids for 6 hours up to 12 hours, usually 4 hours to 8 hours.
It is also an object of this invention to provide a controlled and extended release bupropion capsule formulation that is easy to manufacture and can be used to prepare a range of dosing levels suitable for once daily administration.
It is a further object of the present invention to provide 24-hour control of symptoms of depression or tobacco dependence withdrawal.
Seizures result more commonly by single dosages of bupropion over 150 mg, hence the need for twice to four times daily dosing regimens. Another object of this invention is to provide simplified once daily dosing regimen with the potential to prevent or reduce the incidence of seizures caused by bupropion.
The present invention also relates to a new sustained release bupropion pharmaceutical composition producing novel blood plasma levels after ingestion over 24 hours that is not disclosed in, nor rendered obvious by, the prior art. Other objects, features and advantages of the invention are not taught in the prior art but will be more apparent to those versed in the art from the following specification, taken in conjunction with the drawings.